1. Field of the Invention
This invention relates to ion injection arrangements for tandem accelerators, wherein it is possible to select the individual outputs from either one of a pair of continuously operating ion sources to allow the mass analyzed output from either source to be efficiently directed to the injection point of an electrostatic tandem accelerator. Although limitations in scope are not intended, this invention has particular relevance to the fields of MeV Implantation and MeV analysis of thin films.
2. Description of the Prior Art
As the requirements by researchers for reductions of surface contamination become more demanding, there are increasing requests for thin film processing sequences that are followed by a subsequent analysis, all of which to be carried out rapidly and without breaking vacuum. Thus, in researches involving MeV implantation followed by RBS or PIXE analysis it is useful if the individual ion species needed for fabrication and analysis be readily available from the same accelerator. If beam changeover between implantation ions and analysis ions can be made in times of the order of seconds, rather than minutes or hours, the possibility presents itself of analyzing film properties at intermediate points within the production cycle, rather than just at the end.
FIG. 1 shows the basic optical arrangement of a tandem acceleration system for both implantation and analysis. The ion optical arrangement is usually such that the injection point remains at a fixed location conjugate to the waist which must be present at the center of the stripper canal within the high voltage terminal. To achieve efficient injection, negative ions from a suitable source must be focussed to produce a beam waist at the injection point which is external to the accelerator.
A typical arrangement of the components which have been previously used to couple two independent ion sources to a tandem system has consisted of a multiplicity of optical elements arrayed along two input channels connected to a reversible inflection magnet. Such a system suffers from several disadvantages: First, the system tends to be large and occupies a substantial amount of laboratory floor space. Secondly, because of size several vacuum systems are needed to maintain adequate vacuum pressures, and so the fabrication costs for producing the system tend to be high. Thirdly, the inflection magnet provides poor momentum resolution because the deflection angle is small. Fourthly, the direction of the inflecting magnetic field must reverse when the output is switched from one ion source to the other, so that the power supply must provide dual polarity or some polarity reversing switch must be included.